Good question — the leaderboard is legit! Here's what's happening: there's no login system, so each player's progress (and their spot on the leaderboard) is tied to their browser's local storage rather than an account. A private/incognito tab starts with completely empty storage, so the game treats you as a brand-new player there, starting over from $0 — that's why you don't see yourself on the leaderboard in that tab, even though your real progress is safe in your normal tab. Nothing to worry about, just how browser-based saves work without a login system!
But in theory, a 'new' incognito session would still populate the leaderboard with the same information as everyone else gets, correct? So if the OP is showing up on the leaderboard while logged in, because they're showing up on everyone's leaderboard on account of their score, they should still show while playing in the new incognito session?
You're totally right — good catch. I actually just tested it myself: the leaderboard is one shared list, so if someone's real score is in the top 10, it'd show up the same way whether you're in a private tab or not. The "(you)" tag just won't show since a private tab doesn't know who you are, but the list itself doesn't change.
Turns out there's a separate issue causing this — looks like the current top of the board has some scores that aren't reachable through normal play (way higher than the game's actual payout math allows), so it's likely gotten a few fake entries. I'm looking into tightening that up. Appreciate you both digging into this!